Sulfidation and oxidation resistant cobalt-base alloy



M. S. ROUSH Aug. 27, 1968 SULFIDATION AND OXIDATION RESISTANT COBALT-BASE ALLOY 4 Sheets-Sheet 2 Filed Jan. 25, 1967 Aug. 27, 1968 M. s. ROUSH 3,399,058

SULFIDATION AND OXIDATION RESISTANT COBALT-BASE ALLOY Filed Jan. 25, 1967 4 Sheets-Sheet 4.

2000 (I) O .J

I600 I700 000 I900 2000 TEMPERATURE, F

WEIGHT LOSS MG/SQJN. ALLOY |700F I800F I900F 2000F 0 INCONEL 7:30 400 1252 4200 owl-52 650 I220 3800 VWl-52+3%AL 2l5 410 720 I050 v Wl-52+|/2%Y 200 560 990 |5|5 o Wl-52+3%AL+I/2%Y(ALLOY-Z) 20 I9 3| 35 O ALLOY Z MODIFIED WITH Ni REPLACING ALL OF Co 600 I 810 43 5O SEVERE SULFIDATION TEST INVENTOR MILTON S. ROUSH ATTOR NEYS United States Patent 3,399,058 SULFIDATION AND OXIDATION RESISTANT COBALT-BASE ALLOY Milton S. Ronsh, Phoenix, Ariz., assignor to The Garrett Corporation, a corporation of California Continuation-impart of application Ser. No. 322,096, Nov. 7, 1963. This application Jan. 25, 1967, Ser. No. 617,755

Claims. (Cl. 75170) ABSTRACT OF THE DISCLOSURE A sulfidation and oxidation resistant cobalt-base alloy comprised of a major amount of cobalt, between about 0.05% and 3.0% by weight yttrium, between about 1.0% and 6.0% by weight aluminum and preferably also containing chromium, tungsten and/ or molybdenum, columbium and/ or tantalum and carbon.

This application is a continuation-in-part of my copending application Ser. No. 322,096, filed Nov. 7, 1963, now abandoned.

This invention relates generally to metal alloys and more particularly to alloys provided for use in the manufacture of machine parts, such as gas turbine wheels and/or blades, and nozzle vanes, which are exposed to high-temperature combustion gases containing oxygen, sulfur, lead, and/ or other chemicals that cause oxidation, sulfidation, corrosion and other deleterious effects.

Sulfidation is a metal deterioration which takes place particularly in the heated sections of gas turbines which are exposed to gaseous combustion products of sulfur and/ or lead containing fuels such as fuel oil, diesel fuel, aviation gasoline and the like. The problem is especially serious under desert or salt water atmosphere conditions where the presence of alkali or alkaline-earth metal salts such as sodium chloride, even in concentrations as low as 0.1 part per million, are found to catalyze the sulfidation reaction.

Heretofore, high-temperature metallurgy for use in oxygen containing environments has been limited to: (1) nickel-base alloys which, although oxidation resistant to 2000 F. are not satisfactory in sulfur containing atmospheres over 1650 especially when alkali and alkalineearth metal salts are present, or over 1750 F. when lead deposits are present; and (2) cobalt-base alloys which are resistant to sulfidation and lead attack up to 1850 F. but are not resistant to oxidation above 1750 F. These limitations seriously hamper the development of engines designed to operate with the presently available fuels which burn at 2000 F. or higher temperatures and contain lead, sulfur and other harmful gas-producing matter.

One aim of this invention is to provide an alloy having an equal or better oxidation resisting quality than the high strength nickel-base alloys, such as the alloy known as Inconel 713C, and an equal or better sulfidation resisting quality than the cobalt-base alloys, such as that identified by the trademark WI52.

In research performed prior to the conception of this invention, it was found that small amounts of rare earth metals, as well as yttrium, have been added to cobalt-base and iron-base alloys and as a result the amount of hightemperature oxidation of the alloys was reduced; the

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resistance, but once again the alloys are not resistant to sulfidation.

An object of this invention is to provide an alloy having high resistance to oxidation, sulfidation and lead corrosion when exposed, in oxygen containing environments, to gaseous products of combustion at about 2000 F. temperatures, such as are produced by burning JP4 or other gas turbine fuels.

It has been discovered that the resistance to oxidation, sulfidation and lead corrosion of cobalt-base alloys can be greatly increased by the addition of small percentages of aluminum and yttrium. Y

It is therefore another object of this invention to provide a cobalt-base alloy having at least about 1.0 weight percent aluminum and at least about 0.05 weight percent yttrium to increase the resistance of the alloy to oxidation, sulfidation and lead corrosion when exposed in air to gases resulting from the combustion of JP4 and/or other gas turbine fuels.

Still another object of the invention is to provide a cobalt-base alloy having a maximum of about 6.0 weight percent aluminum and a maximum of about 3.0 weight percent yttrium to further increase the resistance of the alloy to oxidation, sulfidation and lead corrosion when exposed to an atmosphere containing combustion products of fuels of the type employed to operate gas turbine engines.

The superior alloys of this invention are cobalt-base alloys containing a small amount of yttrium and aluminum and preferably a number of other metals which will improve the strength properties of the material. By the term cobalt-base alloy as used herein and as understood in the art, is meant a metallic composition wherein the major element present in cobalt and preferably wherein the cobalt is present in a major amount. More specifically it has been found according to the invention cobalt-base alloys containing from about 0.05 to about 3.0% by weight yttrium and from about 1.0 to about 6.0% by weight aluminum possess outstanding sulfidation and oxidation deterioration resistance.

Preferably the cobalt-base alloys of the invention contain between about 50% and 65% cobalt. In order to provide high strength cobalt-base alloys it is also necessary for the composition to contain tungsten and/or tantalum wherein the total amount of this group of metals is between about 3% and 20% by weight of the alloy composition. The preferred amounts of these metals individually are between 0% and 15% and more preferably between about 4% and 10% individually for tungsten and tantalum with the total amount of this group of metals being no more than about 20% by weight of the alloy composition. Alternatively, molybdenum may be present to replace all or part of the tungsten and columbium may be present to replace a part or all of the tantalum. Molybdenum preferably may be present up to about 10% and columbium up to about 2.0% by weight of the alloy composition. It is also desirable to have chromium present in order to provide a higher strength alloy for many uses. Thus, amounts of chromium up to about 25% and preferably between about 10% and about 25% may be used. The presence of a small amount of carbon also increases the strength of the alloy. However, where the carbon content gets above about 0.5% by Weight oxidation corrosion resistance may be sacrificed somewhat. Thus, suitable carbon concentrations are between about 0.05% and about 0.5% by Weight.

A convenient way to express the concentrations of the preferred cobalt-base alloys of this invention is by mole ratios based on cobalt. Thus, the preferred alloy composi- Patented Aug. 27, 1968 .tions corresponding to the concentrations as set forth above are as follows:

The yttrium used in the alloys of the invention may be pure or may be added as a yttrium composition referred to as a misch metal containing at least about 70% yttrium and a small amount of other elements such as lanthanum, cerium, neodymium, Samarium, gadolinium, dysprosium, erbium, ytterbium, etc., as Well as copper, calcium, magnesium, silicon and the like. When the yttrium is added to the alloy metal it is preferred to use vacuum conditions or those in which oxygen is absent in order to avoid large losses of yttrium due to oxidation.

The following examples are provided to illustrate the manner in which the invention is carried out. Unless otherwise indicated, parts and percents set forth are by weight.

Example I In carrying out the present invention, one of the presently available cobalt alloys, identified as WI-52 and having the following analysis:

Percent C 0.45 Cb+Ta 2.0

Percent Ni 74.2

Ob 2.0 Ti 0.8 A1 6.1

A graph is shown in FIG. 1 having curves to indicate the results of the tests. As shown in the upper left-hand corner of FIG. 1, the following symbols are used to identify the alloys and the curves plotted to illustrate the effect of the test thereon. It will be apparent from the graph that the cobalt alloy WI-SZ, modified to include small portions of both yttrium and aluminum, gained less weight and was therefore more oxidation resistant than the unmodified cobalt-base alloy or the alloy modified by the addition of either of the elements alone. The graph also shows that the alloy WI52 modified by the addition of 1% yttrium and 3% aluminum (designated X) 'has oxidation resisting qualities equal to the nickel-base alloy.

Example II Test samples of the modified cobalt-base alloy X were subjected to sulfidation resistance tests which. were run in an environment consisting of the combustion products of JP4 fuel (CO N 0 H O, S0 at elevated temperatures. After completion of the test the samples are cleaned by boiling in concentrated HNO and wire brushed. The cleaned samples are then weighed to determined any weight change. The results of such tests were compared with the results of similar tests made on the alloy WI-52 without modification and with the addition of a small part of yttrium alone. A chart, identified as FIG. 2 in the drawings, shows the increased resistance to sulfidation secured by the addition of similar small percentages of aluminum and yttrium to the selected cobalt alloy. The chart also shows the results of similar tests applied to samples of the nickel-base alloy Inconel 713C. It is obvious from the chart that the modified cobalt-base alloy X is far superior from a sulfidation resisting standpoint than the nickel-base alloy tested and it is far better than the unmodified cobalt-base alloy.

Example III An accelerated oxidation-sulfidation test procedure was worked out and applied to the cobalt-base alloy WI-52, other cobalt-base alloys available on the market, and certain modified cobalt-base alloys including the one (alloy X) forming the subject matter of the present invention. The nominal chemical compositions of the alloys tested are shown in the chart illustrated in FIG. 3.

The accelerated test procedure was as follows:

The furnace in which the test was to be conducted was purged for thirty minutes with 2.0 c.f.h. N 0.072 c.f.h. C0 and 0.013 c.f.h. H 8. The test specimens were then placed in a silica retort which was in turn placed in the furnace and supplied with a gaseous mixture of 2.0 c.f.h. N 0.072 c.f.h. CO and 0.013 c.f.h. H 8 for two hours. For the following twenty hours the retort was supplied with a mixture of 2.0 c.f.h. air, 0.072 c.f.h. CO and 0.013 c.f.h. S0 Specimens were cleaned and weighed following exposure to temperatures of 17 00 F, 1800 F., and 1900 F. for the twenty-two-hour period. The use of the two cycles during each test closely duplicates a gas turbine start when excess H S is present in the initial combustion products and continuous operation when S0 is found in the gaseous combustion products mixture. The weight losses for the different alloys are shown in the chart illustrated in FIG.-4. These weight-losses are graphically illustrated in FIG. 5 wherein the symbols used to identify the curves and alloys are shown in the upper left-hand corner. It is obvious from this graph that far better sulfidation resistance is secured with the alloy X forming the subject matter of the invention than with any other alloy tested. The graph shows that the addition of small parts of yttrium and aluminum improves the sulfidation resistance of the alloy HS-25, but alloy X is still better. Although this procedure subjected the specimens to more rigorous treatment than the parts of a turbine will normally be subjected to in actual use, the tenst definitely prove the superiority of the newly developed a 0 Example IV The sulfidation test procedure set forth in Example III was repeated with the exception that about 1 p.p.m. NaCl was introduced into the gas stream which contacted the alloy. This was accomplished by bubbling the synthetic gas combustion mixtures through a 10% salt solution. The comparative weight losses for the different alloys tested are set forth and graphically illustrated in FIG. 6.

The sulfidation test procedure set forth in Example IV was repeated. Various alloys were tested with the results total amount of metals of the group is between about 3% and about 20% by weight of the total composition.

6. The composition of claim 5 wherein the respective individual amounts of tungsten and tantalum are between and compositions set forth in the following table: 5 about 4% and 10%, the amount of molybdenum is up to Composition, percent Sulfidation, Alloy wt. loss,

C Cr Ta W Al Y Zr Mn Ni Fe mg./sq. in.,

73. 7 0. 10 20. 0 3.0 0. 45 0. 2. 24 3, 218 62.0 0. 48 20.9 11. 0 3. 1 .1 1 1, 200 73.8 0.10 20. 0 3. 0 1.4 0.40 0.5 0.83 104 70.5 0.10 20. 0 3.0 5.2 0.32 0.5 0.40 13 51. s 0.12 20. 0 9.8 2.4 0.10 0. 5 1.8 46 59.8 0. 11 20.0 14. 9 2. 73 0. 12 0. 5 1.8 80 57. 3 0. 12 20. 0 14. 0 5. 05 0. 0. 5 1. 9 18 69.8 0. 18. 1 3. 7 0. 9 0. 09 0. 19 0. 04 1, 090 69. 4 0. 11 17. 7 3. 7 2. 0 0. 14 0. 24 0. 04 110 03. 6 0.10 17. 6 3.8 2. 9 0.12 0.25 0.04 12 63.2 0. 23 14. 77 10. S8 3. 71 0. 09 0. 11 0. 01 05 50.1 .43 21. 4 15.1 3.2 0.6 0. 22 0. 10 57.8 .43 18.6 11.1 3.1 0. 5 0.19 0. 04 05 0. 19 20. 2 5. 4 3. 5 0. 12 0. 1s 0. 11 4, 270

1 Also contained B (0.004%). 2 Also contained 13 (0.18%).

As is evident from the results of the above-described sulfidation tests, those cobalt-base alloys containing aluminum and yttrium possess vastly superior sulfidation resistance over other alloys including nickel-base alloys containing both aluminum and yttrium. The alloys of the invention may :also contain small amounts of phosphorus and sulfur and preferably in amounts not over 0.04%, silicon in an amount not over about 0.5%. Nickel may be present in amounts up to about 10% as well as iron and manganese in amounts up to about 2.5% in addition to small amounts of zirconium and boron. However, the absence or presence of these elements is not critical or necessary to the alloys of the invention.

The superior sulfidation resistant cobalt-base alloys as disclosed herein may be used for a number of varied purposes. The alloy may be cast, rolled into sheets or prepared as bars or tubing for any uses where superior resistance to sulfur attack as well as oxidation is necessary.

What is claimed is:

1. A sulfi'dation and oxidation resistant cobalt-base alloy comprising a major amount of cobalt and a small effective amount of the metals aluminum and yttrium in combination, the amount of aluminum and yttrium being effective to increase the sulfidation and oxidation resistance of the cobalt-base alloy.

2. The composition of claim 1 wherein the amount of aluminum is up to about 6.0% by weight and the amount of yttrium is up to about 3.0% by weight.

3. The composition of claim 1 wherein the amount of aluminum is at least about 1.0% by 'weight and the amount of yttrium is at least about 0.05% by weight.

4. The composition of claim 1 wherein the amount of aluminum is between about 1.0% and 6.0% by weight andthe amount of yttrium is between about 0.05 and 3.0% by weight.

5. The composition of claim 1 which contains one or more metals selected from the group consisting of tungsten, tantalum, molybdenum and columbium wherein the about 10% and the amount of columbium is up to about 2%.

7. The composition of claim 1 which contains up to about 25% chromium and between about 0.05% and about 0.5% by weight, carbon.

8. A sulfidation and oxidation resistant cobalt-base alloy comprising cobalt, between about 1.0% and 6.0% aluminum, between about 0.05% and 3.0% yttrium, a total amount of between about 8% and 20% of one or more of the metals selected from the group consisting of tungsten, tantalum, molybdenum and columbium, between about 10% and 25% chromium and between about 0.05% and 0.5% carbon, with cobalt being the major metal present and wherein the percents specified are by weight of the total composition.

9. The composition of claim 8 wherein the amount of cobalt is between about 50% and about and wherein the mole ratios of aluminum and yttrium combined to cobalt is between 1:50 and 1:7, chromium to cobalt is between 1:5 and 2:5 and tungsten, tantalum and molybdenum and columbium combined to cobalt is between 1:6 and 1:3.

10. The composition of claim 9 which contains up to the following specified amounts of the following elements: 0.04% phosphorus, 0.04% sulfur, 0.5% silicon, 2.5% iron, 2.5% manganese, 10% nickel, 0.5% boron and 1.0% zirconium.

References Cited UNITED STATES PATENTS 2,304,353 12/1942 Grifiiths et a1 -171 2,513,471 7/1950 Franks et al. 75171 2,513,472 7/1950 Franks et al. 75171 2,703,355 3/1955 Hagglund 75171 2,920,956 1/1960 Nisbet et al. 75171 2,983,602 5/1961 Levinson et al. 75170 2,977,223 3/1961 BrOWn 75171 3,202,506 8/1965 Deutsch 75--171 RICHARD O. DEAN, Primary Examiner. 

